07. Modules

Contents

Way to organize source code, allowing reusability.

Module sources

# On the Terraform registry repo
module "myVpc1" {
  source  = "terraform-aws-modules/vpc/aws"
  version = "5.1.2"
}

# On a Git repository 'git::https://' or 'git::ssh://'
# 'ref' can reference a tag name, a hash or a branch
module "myVpc2" {
  source = "git::https://corporate-gitlab.com/tf-aws-vpc.git?ref=v1.2.0"
}

# Local module ALWAYS starts with './' or '../'
module "instance1" {
  source = "./module-ec2"
}

→ A lot of sources can be used, such as S3 (s3::https://), GCS buckets (gcs::https://), GitHub (github.com/...),...

Key points

A module can be instantiated several times, with a different module instance name

module "myVpc1" {
  source  = "terraform-aws-modules/vpc/aws"
  version = "5.1.2"
}
module "myVpc2" {
  source  = "terraform-aws-modules/vpc/aws"
  version = "5.1.2"
}

Parameters can be provided to a module instance. They are mapped to the module variables

module "myVpc1" {
  source  = "terraform-aws-modules/vpc/aws"
  version = "5.1.2"

  # input variables
  var1 = "val1"
  var2 = "val2"
}

A module can send informations back to its caller using output

# inside the module
output "foo_name" {
  description = "Name of ssth"
  value       = my_object.name
}

# inside the caller
module "module_instance1" {
  source = "../module/my_module"
}

# later, use module.module_instance1.foo_name

Standard module structure

See: Module structure

$ tree minimal-module/
.
├── README.md
├── main.tf
├── variables.tf
├── outputs.tf

$ tree complete-module/
.
├── README.md
├── main.tf
├── variables.tf
├── outputs.tf
├── ...
├── modules/
│   ├── nestedA/
│   │   ├── README.md
│   │   ├── variables.tf
│   │   ├── main.tf
│   │   ├── outputs.tf
│   ├── nestedB/
│   ├── .../
├── examples/
│   ├── exampleA/
│   │   ├── main.tf
│   ├── exampleB/
│   ├── .../

Terraform registry

See: https://registry.terraform.io/browse/modules

Requirements for Publishing Module

GitHub: The module must be on GitHub and must be a public repo. This is only a requirement for the public registry.
Named: Module repositories must use this three-part name format terraform-<PROVIDER>-<NAME>
Repository description: The GitHub repository description is used to populate the short description of the module.
Standard module structure: The module must adhere to the standard module structure.
x.y.z tags for releases: The registry uses tags to identify module versions. Release tag names must be a semantic version, which can optionally be prefixed with a v. For example, v1.0.4 or 0.9.2